1. Field of the Invention
The present invention relates to a piezoelectric resonator containing electrostatic capacitors, and more particularly, the present invention relates to a capacitor-containing piezoelectric resonance component having an improved arrangement of electrodes arranged to define capacitors and spaces for allowing for free and unhindered vibration of the vibration portion of the piezoelectric resonator.
2. Description of the Related Art
Conventionally, capacitor-containing piezoelectric resonance components have widely been used as piezoelectric vibrators. For example, Japanese Unexamined Patent Application Publication No. 7-94997 discloses a capacitor-containing piezoelectric resonance component 201, as shown in FIG. 32. In the capacitor-containing piezoelectric resonance component 201, dielectric substrates 203 and 204 are, respectively, disposed on upper and lower surfaces of a piezoelectric resonance element 202. The piezoelectric resonance element 202 uses one of a thickness-vertical vibration mode and a thickness-extensional sliding mode that are energy-trap type vibration modes. Vibration spaces 205 and 206 are arranged to allow for free and unhindered vibration in the vibrating section of the piezoelectric resonance element 202. In the conventional example, each of the vibration spaces 205 and 206 is defined by a concave section formed in one of the main surfaces of each of the dielectric substrates 203 and 204, respectively.
In the resonance component 201, capacitor-forming electrodes 207 to 209 are disposed on outer surfaces of the layered body defined by the stacked dielectric substrates 203 and 204 to define capacitors. The capacitor-forming electrode 208 is connected to a ground potential. The capacitors are positioned individually between the capacitor-forming electrodes 207 (hot side) and 208 and between the capacitor-forming electrodes 209 (hot side) and 208.
In addition, Japanese Unexamined Patent Application Publication No. 3-240311 discloses a capacitor-containing piezoelectric resonance component 211, as shown in FIG. 33. In the capacitor-containing piezoelectric resonance component 211, dielectric substrates 213 and 214 are disposed on upper and lower surfaces of a piezoelectric resonance element 212. In this conventional example, the dielectric substrates 213 and 214 are individually adhered to a piezoelectric resonance element 212 via insulating adhesive layers 215 and 216, respectively. Vibration spaces 217 and 218 are formed of openings in the respective insulating adhesive layers 215 and 216. Similarly to the capacitor-containing piezoelectric resonance component 201, capacitor-forming electrodes 219 to 221 are disposed on outer surfaces of the layered body including the stacked dielectric substrates 213 and 214 to define capacitors.
In each of the capacitor-containing piezoelectric resonance components 201 and 211, capacitors are individually defined between the intermediate capacitor-forming electrodes 208 and 220 (which are connected to the ground potential) and the oppositely arranged capacitor-forming electrodes 207 and 219, respectively, via a predetermined gap G and between the intermediate capacitor-forming electrodes 208 and 220 and the oppositely arranged capacitor-forming electrodes 209 and 221, respectively, via the predetermined gap G. In these cases, the electrostatic capacitance of each of the capacitors depends on the relative permittivity of the dielectric substrate, the size of the gap G between the capacitor-forming electrodes, and other such factors.
In the capacitor-containing piezoelectric resonance components 201 and 211 described above, however, a problem arises in that the electrostatic capacitance of the capacitors varies according to variations in the positions of the capacitor-forming electrodes 208 and 220.
In order to overcome the problems described above, preferred embodiments of the present invention provide a capacitor-containing piezoelectric resonance component that minimizes and eliminates variation in the electrostatic capacitance.
According to one preferred embodiment of the present invention, a capacitor-containing piezoelectric resonance component includes an energy-trap piezoelectric resonance element having a piezoelectric plate, and a first vibratory electrode and a second vibratory electrode that are individually disposed on portions of two main surfaces of the piezoelectric plate so that a lower surface and an upper surface thereof oppose each other via the piezoelectric plate. A dielectric substrate is disposed on at least one surface of the piezoelectric resonance element with a vibratory space being defined to allow for free and unhindered vibration of a vibrating section. A first capacitor-forming electrode and a second capacitor-forming electrode are arranged on the dielectric substrate so as to oppose each other via a predetermined gap G in a direction that is substantially parallel to the main surface of the dielectric substrate. When Gxe2x80x2 represents the distance between an end portion of the second capacitor-forming electrode and an end portion of the vibration space along the direction in which the first capacitor-forming electrode and the second capacitor-forming electrode oppose each other, at least one of the following expressions is satisfied:
Gxe2x80x2/Gxe2x89xa71 and Gxe2x80x2/Gxe2x89xa6xe2x88x920.4.
As described above, since the ratio Gxe2x80x2/G is within the desired range, even in a case where positions of the first and second capacitor-forming electrodes vary, arranging the ratio of Gxe2x80x2/G to be within the specific range allows the variation in electrostatic capacitance to be significantly reduced. This is especially effective in a case where the position of the second capacitor-forming electrode varies. Therefore, capacitor-containing piezoelectric resonance components having excellent characteristics are easily obtained with this unique construction. In addition, since manufacturing precision of forming the capacitor-forming electrodes need not be improved, productivity of the capacitor-containing piezoelectric resonance component is greatly improved.
According to another preferred embodiment of the present invention, a capacitor-containing piezoelectric resonance component includes an energy-trap piezoelectric resonance element having a piezoelectric plate, and a first vibratory electrode and a second vibratory electrode that are individually disposed on portions of two main surfaces of the piezoelectric plate so that a lower surface and an upper surface thereof oppose each other via the piezoelectric plate. A dielectric substrate is disposed on at least one surface of the piezoelectric resonance element with a vibration space being secured therein for allowing for free and unhindered vibration of a vibrating section of the resonance element. A dielectric layer is disposed between the piezoelectric resonance element and the dielectric substrate and includes an opening provided for defining at least a portion of the vibration space. When xcex51 represents the relative permittivity of the dielectric substrate and xcex52 represents the relative permittivity of the dielectric layer, a relationship xcex52/xcex51xe2x89xa60.063 is satisfied.
As described above, since the xcex52/xcex51 ratio is within the desired range, even in a case where positions of the first and second capacitor-forming electrodes vary, arranging the xcex52/xcex51 ratio to be within the desired range minimizes the variation in electrostatic capacitance to be significantly reduced. Particularly, this is especially effective in a case where the position of the second capacitor-forming electrode varies. Therefore, capacitor-containing piezoelectric resonance components having excellent characteristics are easily obtained. In addition, since precision of the capacitor-forming electrodes need not be improved, productivity of the capacitor-containing piezoelectric resonance component is greatly improved.
According to still another preferred embodiment of the present invention, a capacitor-containing piezoelectric resonance component includes an energy-trap piezoelectric resonance element having a piezoelectric plate, and a first vibratory electrode and a second vibratory electrode that are individually disposed on portions of two main surfaces of the piezoelectric plate so that a lower surface and an upper surface thereof oppose each other via the piezoelectric plate. A dielectric substrate is disposed on at least one surface of the piezoelectric resonance element with a vibration space being secured therein for allowing free and unhindered vibration of a vibrating section of the resonance element. A dielectric layer is disposed between the piezoelectric resonance element and the dielectric substrate and includes an opening provided for defining at least a portion of a vibratory space. A first capacitor-forming electrode and a second capacitor-forming electrode that are provided on the dielectric substrate so as to oppose each other via a predetermined gap G in a direction that is substantially parallel to the main surface of the dielectric substrate. When Gxe2x80x2 represents the distance between an end portion of the second capacitor-forming electrode and an end portion of the vibratory space along the direction in which the first capacitor-forming electrode and the second capacitor-forming electrode oppose each other, xcex51 represents the relative permittivity of the dielectric substrate, and xcex52 represents the relative permittivity of the dielectric layer, at least one of the following relationships is satisfied: xcex52/xcex51 greater than 0.063 and Gxe2x80x2/G greater than 0.2183log(xcex52/xcex51)+1.0682 or xcex52/xcex51 greater than 0.063 and Gxe2x80x2/Gxe2x89xa6xe2x88x920.3756log(xcex52/xcex51)xe2x88x920.5734.
According to the above-described unique construction, since the ratio xcex52/xcex51 and the ratio Gxe2x80x2/G are both within desired ranges, even in a case where positions of the first and second capacitor-forming electrodes vary, arranging the Gxe2x80x2/G ratio to be within the specific range minimizes and eliminates variation in electrostatic capacitance. This is especially effective in a case where the position of the second capacitor-forming electrode varies. Therefore, capacitor-containing piezoelectric resonance components having excellent characteristics are easily obtained. In addition, since manufacturing precision of the capacitor-forming electrodes need not be improved, productivity of the capacitor-containing piezoelectric resonance component is greatly improved.
In the above-described capacitor-containing piezoelectric resonance component, a pair of the first capacitor-forming electrodes may be arranged so as to sandwich the second capacitor-forming electrode in the direction in which the pair of first capacitor-forming electrodes and the second capacitor-forming electrode oppose each other so as to be electrically connected to the piezoelectric resonance element, and the second capacitor-forming electrode is connected to a ground potential.
According to the above-described unique construction, the capacitor-containing piezoelectric resonance component is preferably a three-terminal type wherein one terminal is connected to the ground terminal. Therefore, the capacitor-containing piezoelectric resonance component that greatly reduces the variation in the electrostatic capacitance is provided.
In a capacitor-containing piezoelectric resonance component of various preferred embodiments of the present invention, the dielectric substrate may be disposed on each of two main surfaces of the piezoelectric resonance element with the vibratory space being reliably provided.
The above-described unique construction allows the overlaid-type capacitor-containing piezoelectric resonance component to minimize the variation in the electrostatic capacitance.
Also, the above-described capacitor-containing piezoelectric resonance component may further include a cap-like casing member, wherein the dielectric substrate is larger than the piezoelectric resonance element, and the cap-like casing member is fixed on the dielectric substrate so as to contain the piezoelectric resonance element.
The above-described arrangement provides a capped-type capacitor-containing piezoelectric resonance component that minimizes variation in the electrostatic capacitance.
In addition, the above-described capacitor-containing piezoelectric resonance component may further include a casing substrate that is larger than the dielectric substrate and the piezoelectric resonance element and a cap-like casing member for confining the piezoelectric resonance element and the dielectric substrate, wherein the structure in which the piezoelectric resonance element and the dielectric substrate are overlaid is mounted on the casing substrate, and the cap-like casing member is adhered to the casing substrate.
The above-described construction also allows the provision of the capacitor-containing piezoelectric resonance component that eliminates and minimizes variation in the electrostatic capacitance and that has stable, excellent characteristics. In this case, the capacitor-containing piezoelectric resonance component contains the capacitors defined by the piezoelectric resonance element and the dielectric substrate in a package structure including the casing substrate and the cap-like casing member.
Furthermore, in the above-described capacitor-containing piezoelectric resonance component, the first and second capacitor-forming electrodes may be arranged to oppose each other via the predetermined gap G on an outer surface of the dielectric substrate.
In this case, since the capacitor-forming electrodes are preferably formed only on an outer surface of the dielectric substrate, the capacitor-forming electrodes are easily formed.
Yet furthermore, in the above-described capacitor-containing piezoelectric resonance component, at least one of the first and second capacitor-forming electrodes may be located at an intermediate height in the dielectric substrate to define an inner electrode.
In this case, by controlling the position where the inner electrode is located, a variety of built-in capacitors can be provided, and also, the capacitor-containing piezoelectric resonance component having high anti-moisture characteristics is achieved.
Still furthermore, in the described capacitor-containing piezoelectric resonance component, at least one of the first and second capacitor-forming electrodes may be disposed on a surface of the dielectric substrate on the side where the dielectric substrate is overlaid on the piezoelectric resonance element.
In this case, since the capacitor-forming electrodes can be formed only on an outer surface of the dielectric substrate, the capacitor-forming electrodes can be easily formed.